1. Field of the Invention
The present invention relates to pulverized solid fuel delivery systems and, more particularly, to a nozzle assembly for use in a pulverized solid fuel delivery system.
2. Description of the Related Art
Systems for delivering pulverized solid fuel (e.g. coal) to steam generators typically include a plurality of nozzle assemblies through which pulverized coal is delivered into a combustion chamber of the steam generator. The nozzle assemblies are typically disposed within windboxes, which may be located proximate the corners of the steam generator. Each nozzle assembly includes a nozzle tip, which protrudes into the combustion chamber. Typically, the nozzle tips are arranged to tilt up and down to adjust the location of the flame within the combustion chamber.
One prior art nozzle tip is depicted in FIG. 1, and more completely described in U.S. Pat. No. 6,089,171, entitled “Minimum Recirculation Flame Control (MRFC) Pulverized Solid Fuel Nozzle Tip,” issued Jul. 18, 2000 to Fong et. al, the disclosure of which is incorporated by reference herein, where such disclosure provides a basis for the teachings disclosed herein.
hi FIG. 1, a first embodiment of the MRFC solid fuel nozzle tip 36 includes a secondary air shroud 39; a primary air shroud 40; a secondary air shroud support 50; and splitter plate 51. To facilitate the acquiring of an understanding of the nature of the construction and the mode of operation of the first embodiment of the MRFC solid fuel nozzle tip 36, dotted lines provide a representation of a portion of a fuel compartment 12 and a longitudinally extending portion 38 of the pulverized solid fuel nozzle tip 36. Note the direction of flow of the primary air and pulverized solid fuel is generally depicted by reference numeral 44.
In this embodiment, the secondary air shroud 39 embodies at the inlet end thereof a bulbous configuration 106. The bulbous configuration 106 minimizes bypass of secondary air around the secondary air shroud 39, (i.e., air will not flow through the secondary air shroud 39, particularly under tilt conditions, such as when the secondary air shroud 39 is an upwardly tilt position or a downwardly tilt position relative to the centerline of the MRFC solid fuel nozzle tip 36). Should secondary air bypass the secondary air shroud 39 this also has the concomitant effect of adversely impacting the extend to which the secondary air is capable of carrying out the cooling effect on the secondary air shroud 39 desired therefrom. In addition to the bulbous configuration 106 thereof, the secondary air shroud 39 is further characterized by the embodiment therein of rounded corners, denoted in FIG. 2.
Referring to the embodiment of FIG. 2, a rearward perspective view of the nozzle tip 36 is provided. In the embodiment of FIG. 2, the secondary air shroud 39 includes rounded corners 8. Each of the rounded corners 8 are generally triangular in shape. Assembly of the secondary air shroud 39 calls for separately welding each of the rounded corners 8 into place.
In the embodiments provided in U.S. Pat. No. 6,089,171, the rounded corners 8 of the secondary air shroud 39 are made to embody the same predetermined radius. The rounded corners 8 of the secondary air shroud 39 operate to provide higher velocities in the corners of the secondary air shroud 39, which in turn effectively minimize the existence of low velocity regions on the secondary air shroud 39 that might otherwise lead to unwanted solid fuel deposition.
Although the nozzle tip 36 of the '171 patent has a number of advantages, one skilled in the art will readily surmise, having welded rounded corners 8 may compromise both strength of the secondary air shroud 39 as well as economic construction of the secondary air shroud 39.
Therefore, what are needed are improved techniques for assembly of a secondary air shroud of a nozzle tip, such as the one disclosed in the '171 patent. Preferably, the techniques provide for improved cost of manufacture as well as improved strength.